1. Field of the Invention
The present invention relates to a method for making corrugated fins (hereinafter, simply referred to as fins), for heat exchangers, which each have louvers formed therein.
Note that louvers are formed by cutting part of a fin to let the portions so cut rise in a shutter-like fashion with a view to diverting the direction of fluid flowing around the fin to control the development of a temperature boundary layer.
2. Description of the Related Art
In a common fin making method, strip metal (work) is subjected to press working such as roll forming (refer to JIS (Japanese Industry Standard) B 0122) to be formed into a corrugated configuration while part of the strip metal is being cut and raised into louvers, then the corrugated strip metal is compressed so that the radius of curvature of folded portions (crests and roots) is reduced, and thereafter the strip metal is cut so that each part of the strip metal so cut has a predetermined number of crests (roots).
Incidentally, when strip member comprising a xc2xc H (Hard: Quality discrimination) material or 0(Soft: Quality discrimination) material (refer to JIS (Japanese Industry Standard) H 0500) which is made of a metal such as brass having a relatively low hardness is subjected to press working in order to form the strip member into a corrugated configuration while part of the strip member is being cut and raised into louvers, since the material of the strip member is soft and is easy to elongate, a mold (a cutter) for cutting and raising part of the material into louvers has difficulty in being removed from the strip metal, and as a result, a forming failure is likely to happen easily so that portions of the strip member, where louvers 123 are formed, tend to curve as shown in FIG. 9 or that cracks are generated.
To cope with this, the strip member used to form fins is usually made of a metal having a relatively high hardness such as a xc2xd H (Hard) material or H (Hard) material which has a hardness higher than that of the xc2xc H (Hard) material or 0(Soft) material.
However, when such strip metal having a relatively high hardness is subjected to press working, the force opposing plastic working is increased by work-hardening generated at folded portions (crests and roots) and, therefore, even if the fin is plastically deformed to compress the corrugated strip metal, the radius of curvature of the folded portions (crests and roots) cannot be reduced to a predetermined dimension, this causing a problem that the dimensional accuracy of the fin so formed becomes low.
The invention was made in view of the above problem and the object thereof is to improve the dimensional accuracy of a finished fin which is made of a metal having a relatively high hardness.
With a view to attaining the object, according to the invention, there is provided a method for making corrugated fins for heat exchangers which are formed into a corrugated configuration having a plurality of folded portions (121) and which each have louvers (123) formed in flat flank portions (122) connecting adjacent folded portions (121) by cutting part of the flank portions to let the cut portions rise in a shutter-like fashion, the method comprising a pressing process in which strip metal (W) is subjected to press working so that the strip metal is formed into a corrugated configuration while louvers (123) are being cut and raised in part of the strip metal, a heat treatment process in which residual stress generated in the strip metal (W) is removed after the completion of the pressing process and a compressing process in which the corrugated strip metal (W) is compressed so as to reduce the radius of curvature of the folded portions (121) after the completion of the heat treatment process.
According to the fin forming method, as the residual stress generated in the strip metal (W) is removed by subjecting the strip metal (W), which has gone through the pressing process, to heat treatment, the portions (in particular, the folded portions (123)), which are hardened due to work-hardening, can be softened.
Consequently, as the strip metal (W) which has gone through the pressing process can be easily compressed so that the radius of curvature of the folded portions (121) is reduced to a predetermined dimension, the dimensional accuracy of the finished corrugated fin can be improved even if the fin is made of a metal having a relatively high hardness.
According to the invention, there are also provided a method for making corrugated fins for heat exchangers in which a metal of an iron group is used as strip metal, and corrugated fins are made of the strip metal through processes identical to those of the above fin making method, as well as a method for making corrugated fins for heat exchangers in which a metal of a stainless steel group is used as strip metal, and corrugated fins are made of the strip metal through processes identical to those of the above fin making method, and the same effectiveness provided by the first method can also be provided by the latter two methods.
The present invention will be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.